netdev - [PATCH v2] xfrm: interface: Don't hide plain packets from netfilter

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Date:   Mon,  7 Dec 2020 14:43:09 +0100
From:   Phil Sutter <phil@....cc>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     linux-crypto@...r.kernel.org, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org, Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: [PATCH v2] xfrm: interface: Don't hide plain packets from netfilter

With an IPsec tunnel without dedicated interface, netfilter sees locally
generated packets twice as they exit the physical interface: Once as "the
inner packet" with IPsec context attached and once as the encrypted
(ESP) packet.

With xfrm_interface, the inner packet did not traverse NF_INET_LOCAL_OUT
hook anymore, making it impossible to match on both inner header values
and associated IPsec data from that hook.

Fix this by looping packets transmitted from xfrm_interface through
NF_INET_LOCAL_OUT before passing them on to dst_output(), which makes
behaviour consistent again from netfilter's point of view.

Fixes: f203b76d78092 ("xfrm: Add virtual xfrm interfaces")
Signed-off-by: Phil Sutter <phil@....cc>
---
Changes since v1:
- Extend recipients list, no code changes.
---
 net/xfrm/xfrm_interface.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index aa4cdcf69d471..24af61c95b4d4 100644
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -317,7 +317,8 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 	skb_dst_set(skb, dst);
 	skb->dev = tdev;

-	err = dst_output(xi->net, skb->sk, skb);
+	err = NF_HOOK(skb_dst(skb)->ops->family, NF_INET_LOCAL_OUT, xi->net,
+		      skb->sk, skb, NULL, skb_dst(skb)->dev, dst_output);
 	if (net_xmit_eval(err) == 0) {
 		struct pcpu_sw_netstats *tstats = this_cpu_ptr(dev->tstats);

-- 
2.28.0